Conventional local area networks come in two primary configurations, ring and multi-drop configurations. In a ring configuration, messages are passed from one node in the network to the next until they reach their destinations. Since a given node transmits a message directly to only the next node in the ring network, there is no possibility of message contention (collision) on a given internodal link. The drawback of the ring configuration is that not all nodes on the network can listen to a transmitted message simultaneously (i.e., it is not possible to "broadcast" the message to several nodes at any one given time).
In a multi-drop configuration, a single hardware bus unites all the nodes together. This allows the message transmitted by a single node to be received by all the other nodes simultaneously, a desirable feature in many real-time applications (e.g., such as in radio frequency communication systems which require messages to be sent to several repeaters in the system at approximately the same time). The drawback to this configuration, however, is that it is entirely possible for two or more nodes in the network to transmit a message simultaneously, causing message contention (collision) which results in corruption of the transmitted messages.
Other fairly elaborate LAN protocols, such as Carrier Sense Multiple Access (CSMA, such as found in Ethernet), Token Bus (involving passing a token in a message frame), and Arbitration by Master, among others, have been developed to minimize the contention that could occur on the LAN buses. The problem with most of these more sophisticated protocol networks is that they involve using expensive circuitry and IC's (such is the case with Ethernet and Token Bus configurations), or relatively complex software (such as with Arbitration by Master configurations) which result in expensive networks and/or long handshaking delays.
Presently, several types of local area networks are used in communication networks, with some of the more frequently used LANs being the Ethernet, Token Bus, LocalTalk and Token Ring networks. The Ethernet LAN uses a multi-drop configuration which employs a carrier sense multiple access contention scheme (CSMA) which minimizes collisions on the bus. Ethernet has a drawback in that it does not eliminate collisions entirely, something which is not acceptable in many communication systems. Ethernet systems typically employ a two conductor cable for operation. The Token Bus network is also a multi-drop network, the Token Bus however employs message embedded token passing to avoid collisions on the bus. Token Bus networks also employ two conductor cables, but require sophisticated electronics and software to implement the embedded token passing scheme.
The LocalTalk network is also configured as a multi-drop system but employs a software handshake protocol between the message source node and the destination node. LocalTalk networks require sophisticated software to implement the handshake routines. These handshakes reduce the maximum effective information transfer rate for the network. Finally, Token Ring networks avoid all contentions between communication nodes wanting to transmit messages at the same time by passing a token from node to node. However, the Token Ring network is not able to support broadcasting of messages to more then one node at a given time, a major drawback to systems which require messages to be sent to several nodes at one time.
A need thus exists for a contention free local area network which can be implemented without using complex hardware and/or software, which adds considerable cost to a communication system. The local area network should also be transparent to software and provide for high network utilization. The LAN should also allow for network efficiency not to be compromised when the network has a large number of nodes, and allow for the broadcasting of messages to more than one node at any given time.